Alcoholism is the cause of widespread social and human health problems. Alcohol sensitivity, the development of tolerance to alcohol, and susceptibility to addiction varies among individuals. This variation is attributable to segregating alleles at multiple interacting genes with small effects, whose expression is sensitive to environmental factors. Determining what genetic factors affect variation in alcohol sensitivity, tolerance and addiction is challenging in humans, but can be addressed more readily in genetic model organisms. The long-term goal of this project is to understand the quantitative genetic architecture of sensitivity and tolerance to ethanol, using Drosophila melanogaster as a model system. The short-term goals for this two-year exploratory R21 proposal are (1) to identify new candidate genes and pathways regulating alcohol sensitivity and tolerance; and (2) to map quantitative trait loci (QTLs) affecting naturally occurring variation in these traits with high resolution. We will screen ca. 800 co-isogenic P-element insertion lines to identify genes affecting alcohol sensitivity and tolerance, and couple this screen with gene expression analysis to expand the known collection of genes that contribute to these traits. We will also perform high resolution QTL mapping studies on a series of isogenic recombinant introgression lines to identify chromosomal regions and genes that contribute to variation in ethanol sensitivity; and screen a collection of 300 inbred lines recently derived from nature for ethanol sensitivity and tolerance to identify extreme lines for subseqeunt QTL analyses. These studies will provide the preliminary data for a full R01 application in which we will propose to fully characterize the candidate genes implicated by these studies. Given the evolutionary conservation of important biological processes across taxa as diverse as yeast, nematodes, Drosophila, mice, and humans, genes and pathways discovered in model organisms can be incorporated as candidate genes in human linkage and association studies.